Rock discontinuities such as joints widely exist in natural rock masses, and wave attenuation through rock masses is mainly caused by discontinuities. The displacement discontinuity model (DDM) has been widely used in theoretical and numerical analysis of wave propagation across rock discontinuity. However, the circumstance under which the DDM is applicable to predict wave propagation across rock discontinuity remains poorly understood. In this study, theoretical analysis and ultrasonic laboratory tests were carried out to examine the theoretical applicability of the DDM for wave propagation, where specimens with rough joints comprising regular rectangular asperities of different spacings and heights were prepared by 3D printing technology. It is found that the theoretical applicability of the DDM to predict wave propagation across rock discontinuity is determined by three joint parameters, i.e. the dimensionless asperity spacing (L), the dimensionless asperity height (H) and the groove density (D). Through theoretical analysis and laboratory tests, the conditions under which the DDM is applicable are derived as follows: L≤−0.21D+0.27 and H≤−0.12D+0.17, D∈(0,1]. With increase in the groove density, the thresholds of the dimensionless asperity spacing and the dimensionless asperity height show a decreasing trend. In addition, the transmission coefficient in the frequency domain decreases with increasing groove density, dimensionless asperity spacing or dimensionless asperity height. The findings can facilitate our understanding of DDM for predicting wave propagation across rock discontinuity.

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Keywords: Displacement discontinuity model, Wave propagation, 3D printing, Joint stiffness, Joint roughness